in lower daily doses say 12.
5 to 25 mg can help prevent colds by keeping immune functions balanced. But, too much zinc can be toxic long term. In an acute situation with a cold that has started 25 mg in lozenge form slowly dissolved in the mouth can shorten a colds duration and severity. The lozenge route is only one that works well as this is a local mucosal event, pills don't work well.